It has long been known that the bast fibers of various plant materials, e.g. flax, jute, hemp, ramie, kenaf, have particular utility in a wide variety of textile and industrial uses. Accordingly, many different types of machines have been used to process the material for separating the bast fibers of the plant material from the woody portions thereof. For example, machines that utilize a scutching or beating or flailing action as the primary mechanism to break-up the woody material for dislodging it from associated fibers are well-known in the art.
A problem arises with the above-referenced processes in that they can tend to undesirably damage or shorten the fibers as they are being separated from the woody portions of the plant material and thereby yield a product that has fibers that are shortened beyond their optimum length for maximizing their commercial value. This is a particular problem in processing flax that is harvested for its seeds to produce linseed oil such as grown in North America. The North American strain of flax straw is a shorter plant that matures earlier so that it is cheaper to grow than the longer strains of flax straw which are specifically grown for fiber production, such as in Europe. Accordingly, processing flax straw, particularly of the North American strain requires that the woody portions or shive be separated from the flax fibers without a substantial shortening of the flax fibers given the short length of the flax straw to begin with. However, the equipment employed for this process is typically not specifically designed to handle the short North American strain of flax straw and generally causes too much shortening of the fiber rendering it less desirable for many commercial applications and difficult to process in terms of separating out the shive therefrom. Because of this, in most instances where the flax plant is cultivated for its oilseed in North America, there is no attempt made to process the flax to obtain the fibers therefrom. In 1996 in Canada alone, 2.2 million acres of flax straw were grown. As only approximately 10-20% of this acreage of flax was used for paper processing, it can be seen that there is a huge amount of untapped flax fiber that is not currently being used because of the above-described processing limitations.
The stalk of the flax plant has about 30-40% long outer bast fibers and 60-70% short woody inner core fibers or shives. The shives are left as a by-product when the flax material is processed to separate the fibers therefrom. Accordingly, the majority of the flax plant is left as a low-cost reject that is disposed of without any appreciable commercial gain such as by supplying it to farmers for livestock bedding, or for piling it along treelines as biomass to mix with soil and for stopping weed growth. In this regard, sale of shive material only takes in around $9 per ton. Shive has also been used in some board making, and pulp and paper applications.
The size of the shive separated by flax processing equipment from the fibers thereof can vary widely from small to large pieces of shive. In most current applications for shive, the size of the shive is not critical such that the variations in shive sizes as produced by current flax processing equipment are not an issue. On the other hand, applicants have found that shive that is ground to a fine, consistent size can be used in polymer composite applications as either a filler or a reinforcement additive. As opposed to most current applications where shive is utilized, the size of the shive can be critical in composite applications making the consistency of the small shive particles important.
Thus, it can be seen that there is a need for a plant material processing system, and particularly one that processes the short, tough North American strain of flax grown for its oilseed, that is effective to separate the fibers from the shive thereof without undesirably damaging and shortening the fibers. Further, there is a need for a processing system which can take the shive separated from the flax fibers and reduce it to a very fine, consistent size which has found particular utility in composite applications.